A dynamic voltage restorer with an improved PLL for voltage sensitive loads

Dynamic Voltage Restorers (DVR) are commonly used in the distribution network to protect voltage sensitive loads from the effects of voltage sags, swells and imbalances. This paper presents the modelling and control principle of a battery based DVR. The energy storage element is used to absorb and inject active power during steady-state operation. Finite Impulse Response(FIR) filter based PLL is used for generating a reliable voltage reference. The control strategy uses an inner current control loop and an outer voltage control loop for generating the inverter switching pulses. The performance of the system is investigated by MATLAB simulations and is validated using experimental results obtained from a 230 V system equipped with a 60 V/60 V, 1 kVA injection transformer. The response of the DVR to various voltage disturbances are presented.